If a layout is
specified, all rendered actions will have their result rendered when the layoutyields. This layout can
itself depend on instance variables assigned during action performance and
have access to them as any normal template would.

Worth noting that if you have a controller which inherits from another
controller which has a layout, and in this child controller you’re
determining the layout at
runtime using a method for specific actions, the other actions you are
excluding will not inherit the layout from
the parent controller.